Burner for atomic absorption spectroscopy

ABSTRACT

A SCIENTIFIC BURNER FOR USE IN ATOMIC ABSORPTION SPECTROSCOPY HAS A HOLLOW, CYLINDRICAL BODY PROVIDED WITH TWO LATERALLY SPACED, LONGITUDINALLY EXTENDING ROWS OF OUTLET HOLES AND A SINGLE, LONGITUDINALLY EXTENDING OUTLET SLIT DISPOSED CENTRALLY BETWEEN THE TWO ROWS OF HOLES. THE SIZE OF THE HOLES AND THE SIZE OF THE SLIT AS WELL AS THE RELATIVE SPACING THEREBETWEEN PERMITS THE BURNER TO SUPPLY INDIVIDUAL, LOW INTENSITY REDUCING FLAMES IN ADDITION TO A SINGLE, HIGH INTENSITY OXIDIZING FLAME, AND FREEDOM FROM INTERNAL PLATES AND LIKE STRUCTURE WITHIN THE CHAMBER OF THE BURNER ELIMINATES THE POSSIBILITY OF PREIGNITION OR FLASHBACK. REMOVABLE PLUGS AT OPPOSITE ENDS OF THE CHAMBER PROVIDE ACCESS TO THE LATTER FOR THOROUGH CLEANING, AND THE SMOOTH, ARCUATE CONFIGURATION OF THE CHAMBER WALL FACILITATES COMPLETE REMOVAL OF ALL CONTAMINANTS THEREFROM AFTER EACH ANALYSIS.

United States Patent [191 Wang [ BURNER FOR ATOMIC ABSORPTION SPECTROSCOPY [76] Inventor: Maw Shiu Wang, 1573 Ross, St.

Louis, Mo. 63141 [22] Filed: June 12, 1972 [21] Appl. N0.: 262,154

Primary Examiner-CarrOll-B. Dority, Jr.

Attorney, Agent, or Firm-Gordon D. Schmidt et al.

Q OOOOOOOOOOOOOOOOOOOOOO OOOOOOOO [57] ABSTRACT A scientific burner for use in atomic absorption spectroscopy has a hollow, cylindrical body provided with two laterally spaced, longitudinally extending rows of outlet holes and a single, longitudinally extending outlet slit disposed centrally between the two rows of holes. The size of the holes and the size of the slit as well as the relative spacing therebetween permits the burner to supply individual, low intensity reducing flames in addition to a single, high intensity oxidizing flame, and freedom from internal plates and like structure within the chamber of the burner eliminates the possibility of preignition or flashback. Removable plugs at opposite ends of the chamber provide access to the latter for thorough cleaning, and the smooth, arcuate configuration of the chamber wall facilitates complete removal of all contaminants therefrom after each analysis.

10 Claims, 4 Drawing Figures OOOOOOOOOOOOOOOOOOOOOOOOOOOO PATENTED I974 3.826.432

26 000/000OOOOOOOOOOOOOOOOOOOOOOOOO O OOOOOOOOOOOOOOOOOOOOOO OOOOOOOO BURNER FOR ATOMIC ABSORPTION SPECTROSCOPY This invention relates to the highly specialized and technical field of atomic absorption spectroscopy and, more particularly, to an improved scientific burner for use in connection therewith.

in atomic absorption spectroscopy a mixture of gas fuel, air, and nebulized material to be analyzed is introduced into a special burner and then ignited as the mixture issues from the burner. A light source is positioned to direct a beam across a portion of the flame thus produced into a special light-sensitive receiver which monitors the amount of light absorbed by the flame, thereby determining quantitatively the concentration of the test material.

The above procedure is extremely sensitive to the conditions under which the analysis is carried out, particularly where trace impurities in low concentrations are involved. In this respect, it is imperative that the characteristics of the flame or flames produced by the buner remain uniform throughout the entire analysis such that an accurate determination as a function of time may be obtained. If the flame is unstable with periodic fluttering (which may be caused, for example, by turbulence in the fuel flowing from the burner), the stationary light beam may pass through several different portions of the flame throughout the analysis or may even be disposed outside of the flame from time to time, thereby failing to be absorbed by material actually present in the flame which, of course, produces a false determination of the concentration of material present.

Another source of fluctuation in flame characteristics is termed misalignment. During prolonged operation of the burner, its constituent parts necessarily become heated to a high degree and may become warped or distorted, such warpage being particularly serious in the area surrounding the outlet of the burner because such area determines the size, shape, and position of the flame. The flame may thus be displaced with respect to the light beam as the analysis progresses, thereby producing an inconsistent absorption rate which results in an analysis of questionable accuracy. Manifestly, the problem of misalignment is increased in those situations in which the flame is elongated in nature by virtue of the slotted configuration of the outlet through which the fuel mixture issues. Warpage of the metal defining the slot may occur in an irregular fashion along its length, thereby producing an uneven outermost margin in the continuous flame which may result in a hit-and-miss operation of the beam.

Prior scientific burners were not capable of maintaining constant test conditions from initiation of the analysis until a determination was completed. Moreover, prior burners were subjct to flashback or preignition. In this latter respect, some materials may be analyzed only in the presence of a relatively low intensity reducing flame which does not appreciably overheat the burner itself, while others require a high intensity oxidizing flame which, if the burner is not properly designed, may cause the burner to reach the igniton temperature of the fuel mixture and preignite the same internally of the burner before it can issue through the outlet. This phenomena so completely disrupts the analysis that in many instances it was simply not practical to test materials requiring a severe oxidizing flame. It should also be noted that oxidizing flames increase the likelihood of warpage and its attendant problem of misalignment.

In certain prior burners the flashback problem is particularly severe. These are the types which are provided with a single, rectangular, fuel mixture outlet that is subdivided by a plurality of internal plates into side-byside outlet slits. Because the plates are disposed internally of the burner, they are in strategic position to contact the mixture before it issues from the burner and hence are perfectly located to transmit heat to the mixture, thereby greatly increasing the likelihood that flashback will occur.

Moreover, because such plates are inherently thin and are individual members not integral with the remaining body of the burner, they cannot readily dissipate the heat transmitted thereto so that heat buildup occurs at a rapid rate. This, of course, makes the plates more susceptible to distortion as well as to flashback.

A further problem which has existed with previous burners used in this field has been the memory effect created by residue accumulated in the burner and then carried over from one analysis to another. Those burners having internal plates are especially notorious in this respect because of their inherent resistance to thorough cleaning. Assemblies of rivets and spacer washers have been used to support the plates, producing extensive clutter upon which residue may accumulate. Contaminant carry over from one analysis to the next is especially serious where trace impurities in low concentrations are being analyzed.

Accordingly, in view of the above considerations and deficiencies in prior art scientific burners for atomic absorption spectroscopy, it is an important object of the present invention to provide a scientific burner of the aforesaid type which is highly sensitive in that it is capable of producing a low intensity reducing flame as well as a high intensity oxidizing flame, yet is com pletely flashback-free, even during severe oxidizing situations.

A more specific object in accordance with that set forth above is to provide a burner as aforesaid having a cylindrical, hollow body which is provided with two laterally spaced rows of outlet holes and a single outlet slit disposed therebetween centrally thereof, the slit and holes thus cooperating to provide the highly desirable flame characteristics above set forth.

Another more specific object of the present invention is to provide such a scientific burner wherein flashback is eliminated by virtue of the fact that the chamber of the burner is completely devoid of internal guide structure such as plates and the like, such that heat transmitted to the chamber is held below the ignition point of the fuel mixture.

Another important object of the instant invention is to provide a scientific burner for atomic absorption spectroscopy which eliminates the problem of misalignment resulting from heat induced distortion of slitdefining plates and like structure in prior art burners by having a burner outlet which is formed in integral portions of the body of the burner itself without extraneous memers of any kind whatsoever.

An additional important object is to provide a scientific burner as aforesaid which is capable of producing a highly stable flame for prolonged periods of operation free of fluttering and flickering such as may otherwise be caused by impediments to laminar flow.

Another important object of the instant invention is to provide a burner as aforesaid having a smooth, uniformly arcuate chamber wall which may be thoroughly and readily cleaned without excessive time and effort in order to eliminate any carryover of contaminants from one analysis to another.

In the drawing:

FIG. 1 is a top plan view of a scientific burner constructed in accordance with the teachings of the present invention;

FIG. 2 is a side elevational view with its cylindrical body partially broken away and shown in cross section to reveal details of construction;

FIG. 3 is a vertical, cross-sectional view of the burner taken along line 33 of FIG. 2; and

FIG. 4 is an enlarged, fragmentary, cross-sectional view through the chamber wall of the burner illustrating the relationship of the central outlet thereof to its adjacent outlet holes.

Burner has a hollow, cylindrical body 12 defined by a continuous arcuate wall 14 which encloses a chamber 16. The opposed open ends of body 12 are removably closed by a pair of plugs 18, each of which is provided with an annular sealing ring which fits into pressure contact with the proximal wall 14.

An opening 22 midway between the opposed ends of body 12 at the bottom thereof communicates with a tube 24 to present an inlet into chamber 16 for a mixture of air, gas fuel, and neubulized material to be analyzed. Directly across from the inlet defined by opening 22 and tube 24 are outlets defined by a slit 26 extending longitudinally of body 12 and two rows of circular holes 28 also extending longitudinally of body 12 on opposite sides of slit 26. Slit 26 is disposed centrally of the rows of holes 28 and, as shown best in FIGS. 3 and 4, has its center line disposed in the same vertical plane as that of opening 22. Moreover, holes 28 extend nonradially through wall 14 in parallelism wiht one another and with slit 26 toward the floor of chamber 16.

As shown best in FIG. 1, the rows of holes 28 extend substantially the full length of slit 26, there being 32 of the holes 28 spaced equally apart in each row. The slit 26 is preferably 10 cm. in length and may be within the range of 0.010 to 0.020 inches in width. The distance from the center line of slit 26 to the center line of each row of holes 28 may be from 0.070 to 0.125 inches, and each hole 28 may be from 0.030 to 0.080 inches in diameter. A preferred set of dimensions for burner 10 providing optimum results are 0.015 inches for the width of slit 26, 0.070 inches for the distance between the center line of slit 26 and the center line of each row of holes 28, and 0.052 inches for the diameter of each hole 28.

As shown best in FIGS. 2 and 3, the interior surface of wall 14 is smooth and uncluttered, free from projections and surface irregularities. Moreover, no structure is located between inlet opening 22 and the outlets defined by slit 26 and holes 28. A plurality of rectangular cooling fins 30 embrace body 12 and are spaced longitudinally along the latter for dissipating heat from chamber 16.

In operation, a mixture of air, gas fuel, and nebulized material to be analyzed enters chamber 16 through tube 24 and opening 22 for subsequent passage through each hole 28 and slit 26. A plurality of individual, flame-supporting streams are thus produced by holes 28, and an elongated, generally planar, flamesupporting stream is produced by slit 26. Ignition of these streams produces flames suitable for analysis of the neubulized material.

Because of the size, configuration, and spacing of holes 28 relative to one another and to slit 26, burner 10 is capable of an extremely high degree of sensitivity. At one extreme, such as where the material being analyzed requires a reducing flame of low intensity, the individual streams issuing from holes 28 permit the formation of sixty-four individual, low intensity flames plus the central flame from slit 26. In this manner, burner 10 may be readily aligned with respect to its light source so that the light beam is directed across any one or combination of flames from holes 28 as required. Note that by aligning burner 10 so that the light beam extends longitudinally of a row of holes 28, the beam may be directed through all thirty-two flames of the row or, by canting burner 10, the light beam may be directed across just one of such flames.

At the other extreme, the individual streams issuing from holes 28 and from slit 26 may be merged together to produce a single high intensity oxidizing flame for use with materials requiring a flame of such character. While holes 28 are sufiiciently spaced from one another and from slit 26 to produce the individual reducing flames if such is desired, nonetheless, their spacing is not so great that an oxidizing flame cannot be produced. I

The specific dimensions for holes 28 and slit 26 are carefully selected in order to obtain the desired result and are based in part on the desired velocities of the streams which will issue from slit 26 and holes 28, as well as on sensitivity requirements. If the dimensions selected fall outside of the ranges hereinabove set forth, it is likely that an imbalance in flame characteristics may result between the three lines of flames. It is important that burning chemistry across the three lines of flames be identical for identical reduction or oxidation.

It is especially noteworthy that even when an oxidizing flame is produced, there is no danger whatsoever of preignition or flashback within chamber 16. This is true in spite of the extremely high temperatures which are produced by such oxidizing flames. Prior burners employing internal divider plates to define fuel outlet slits have not been able to avoid this problem because, as explained earlier, such plates heat the mixture to its ignition point before it can reach the outlets, thereby causing the burner to flashback and totally disrupt the analysis.

In contrast to this type of arrangement, chamber 16 of burner 10 is completely devoid of internal divider plates or like structure such that heat is not transmitted from the hot burner surfce down to chamber 16. The guiding and directing means for the mixture from chamber 16 are integral areas of wall 14 which surround and define slit 26 and holes 28.

Another important distinction between burner. 10 and prior art burners which utilize divider plates is the ability of burner 10 to eliminate misalignment and to produce extremely stable flames throughout the entire analysis. In this respect, the flames from holes 28 and slit 26 are not displaced relative to one another because of heat-induced warpage, nor do they flutter and flicker. While the divider plates of earlier burners expanded so that the dimensional tolerances of their slits were not maintained, the absence of such plates in burner 10 assures that the dimensional tolerance of slit 26 and holes 28 will not be exceeded. The use of holes 28 in lieu of additional slits is especially important in this respect since a greater amount of material is thereby left intact in the outlet area to lend structural rigidity to wall 14 and to resist deformation upon heating. Such maintenance of dimensional tolerances is extremely important because of the high degree of accuracy required during analysis. As hereinabove explained, any displacement of the flame or flames throughout the period of analysis has a corresponding effect upon the amount of light absorbed, hence producing a false report of the true concentration of mate rial being analyzed.

Freedom from fluttering is obtained by virtue of the steady, unimpeded flow of streams through slit 26 and holes 28. Once again, the elimination of divider plates and the like within chamber 16 is important because such plates require rivets, spacer washers and the like for support, and such rivets and washers present obstruetions to laminar flow to thereby create turbulence and a lack of flame stability.

Access to chamber 16 for cleaning purposes may be easily gained after each analysis by removing end plugs 18. In this manner, the smooth arcuate, inner surface of wall 14 may be thoroughly cleaned to remove any and all traces of material from the preceding analysis. Likewise, slit 26 and holes 28 may be readily cleaned to remove particles which would contaminate subsequent analyses. Note that the lack of projecting structures of any kind within chamber 16 and freedom from depressions in the inner surface of wall 14 facilitate cleaning and increase the likelihood that all residue will be completely removed to prevent any carry-over contamination.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

l. A highly sensitive, flashback-free burner for atomic absorption spectroscopy capable of maintaining constant, uniform flame characteristics throughout prolonged burner operation for monitoring elemental concentrations as a function of time, said burner comprising:

an elongated, hollow body having a chamber for a combustible gas fuel;

an inlet communicating with said chamber for supplying fuel to the latter;

a pair of laterally spaced-apart, longitudinally extending rows of outlet holes in said body communieating with said chamber for discharging individual falme-supporting streams of fuel from the body; and

an elongated outlet slit in said body disposed between said rows centrally thereof and extending longitudinally of the body in communication with said chamber for discharging a flame-supporting, generally planar stream of fuel from the body in addition to those streams provided by said holes,

said holes being spaced from one another and from said slit an amount which, at one extreme, permits the formation of individual, relatively low intensity reducing flames from each of said holes and from said slit, and, at the other extreme, permits the formation of a single, relatively high intensity oxidizing flame produced by the mergence of fuel streams from said slit and said holes.

2. A burner as claimed in claim 1, wherein said body is devoid of structural members or projections within said chamber between said inlet and the outlets.

3. A burner as claimed in claim 1, wherein said rows of holes are substantially coextensive with said slit.

4. A burner as claimed in claim 1, wherein said body is cylindrical in configuration having a continuous arcuate wall defining said chamber, said holes and said slit extending through said wall.

5. A burner as claimed in claim 4, wherein said holes extend non-radially such that the holes of one row are disposed in parallelism with the holes of the other row.

6. A burner as claimed in claim 5, wherein said inlet includes an opening in said wall on the opposite side of the chamber from said holes and said slit for issuing fuel directly to the holes and the slit.

7. A burner as claimed in claim 6, wherein said wall, said holes and said slot are devoid of structural projections and recesses to prevent residue accumulation.

8. A burner as claimed in claim 1, wherein said slit is within the range of 0.010 inches to 0.020 inches in width.

9. A burner as claimed in claim 8, wherein said holes are each circular in configuration and are within the range of 0.030 inches to 0.080 inches in diameter.

10. A burner as claimed in claim 9, wherein the distance from the center of said slit to the line of centers of each row of said holes is within the range of 0.070

inches to 0.125 inches. 

